Slight surging while decelerating / coasting

[stuntmanmike]

Originally Posted by S.hafsmo

Closed throttle, in gear. At lest in my case. Also in the transition between closed and slightly applied throttle.

Exactly, closed throttle in gear. OK cool, seems like nothing is wrong with the car if others experience this! Thanks

[Paul Workman]

Originally Posted by XfireZ51

I’ll bet that if u have a fairly stock calibration and have ur car freewheeling down to a stop, that the surging stops at 5mph.

Ya know...I just realized that I also converted my FW to a Fidanza at the same time I installed my SW headers...when the surging first appeared. Hmmm....

NOT intending to hijack the thread, but my Z surges on decel a little too, and the Fidanza FW thing is just another "potato" for the stew pot!

[S.hafsmo]

Mine is all stock clutch/flywheel wise. But some monkey amongst the previous owners did cut away the resonator to make way for nasty welding and straight pipes (I see most others has a cat-back or more).

And the issue isn't really when coasting to a stop, but when letting off the throttle due to a downhill descent or any similar reason you'd want to slow down a bit (annoying people in the way, for instance).

[jss06c6]

My '91 had a "hunting" rpm upon deceleration with clutch in and Fidanza FW. Like Dom said mine went away at about 3-5 mph. I changed back to dual mass setup and the "hunting" has all but vanished. Nothing else was changed. Just a data point from my experience.

Since the engine is unloaded with clutch in, the anomaly is tied to vehicle speed and I would guess could be addressed in the tune. My situation wasn't bad enough to chase in my tune. This was present with both Marc's tune and my revised tune. Never had stock tune loaded to compare.

Sent from my XT1585 using ZR-1 Net Registry mobile app

[XfireZ51]

Originally Posted by jss06c6

My '91 had a "hunting" rpm upon deceleration with clutch in and Fidanza FW. Like Dom said mine went away at about 3-5 mph. I changed back to dual mass setup and the "hunting" has all but vanished. Nothing else was changed. Just a data point from my experience.

Since the engine is unloaded with clutch in, the anomaly is tied to vehicle speed and I would guess could be addressed in the tune. My situation wasn't bad enough to chase in my tune. This was present with both Marc's tune and my revised tune. Never had stock tune loaded to compare.

Sent from my XT1585 using ZR-1 Net Registry mobile app

It comes down to this. When you play w the LT5 configuration, the stock tune is "built" to manage the motor as is. Change that and the values of the parameters end up overdoing the compensations that are built in. Enhancing fuel and airflow etc. really requires a toning down of the tune if that makes sense. Otherwise the stock tune will compensate to the level of de-stabilizing the motor. So, as an example, the stock cal will reduced timing by "x" if idle is too high. On a modified motor, you want to reduce the amount of timing taken out to achieve this, otherwise the stock reduction can kick in the stall saver and now you have a see-saw idle.
In the case of an oscillating free-wheeling idle, one thing to modify is by bringing in Closed Throttle spark advance sooner rather than the stock 5mph.

[jss06c6]

Had not looked at the Closed Throttle Spark Advance Dom.. I don't have an issue but will look at the value in my tune. Thanks!

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[rkreigh]

try tuning the DFCO the stock car calibration cuts the gas for mileage and this can lead to some slight rubber banding and bucking on decal.


if you have a light flywheel the loss of decal intertia has an impact on the smoothness as well


it's not a problem. and tuning can smooth this out in many cases unless you swapped the flywheel and then it's much trickier IMHO

[BurnRubber]

My car is bone stock with only 15000 miles and it sometimes hunts on clutch in and engine decelerating. Sounds like there may be some hiccups in these speed density computers.

[tiegsd]

I have the same minor "surging" in gear during decel. My 90 is stock other than Haibeck chip. Always smooth otherwise in gear, figured it was just normal adjustments by ecu. Feels a bit like my MV Augusta motorcycle when the compression release kicks in on closed throttle.

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[stuntmanmike]

Drove the Z for 200 miles this weekend and found myself putting car in neutral more than I'd like to avoid this phenomenon. The car rips when on the gas.

This is a California car and when I put the Haibeck chip in I didn't remove the old one, was a "piggy back" situation I believe, wonder if CA-delivered cars have extra smog equipment that could be contributing?

Can you recommend anyone in NY metro area that is an expert in tuning ZR1s? Would like to try changing closed throttle spark advance as suggested above but no idea how to mess with that. Thanks